Mail processing systems, such as, for example, a mailing machine, often include different modules that automate the processes of producing mail pieces. The typical mailing machine includes a variety of different modules or sub-systems, each of which performs a different task on the mail piece. The mail piece is conveyed downstream utilizing a transport mechanism, such as rollers or a belt, to each of the modules. Such modules could include, for example, a singulating module for separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a stripping/moistening module for stripping open the flap of an envelope and wetting and sealing the glued flap of an envelope, a weighing module for weighing the mail piece, and a metering/printing module for storing postage amounts and applying evidence of postage either directly to the mail piece or to a tape to be applied to the mail piece. The mailing machine is controlled by a central processing unit that executes software stored in memory provided in the mailing machine. The exact configuration of the mailing machine is, of course, particular to the needs of the user.
The metering/printing modules of many current mailing machines utilize ink jet printing technology to print evidence of postage, such as postal indicia. Generally, an ink jet printer includes one or more arrays of nozzles (sometimes referred to as orifices), a supply of ink, a plurality of ejection elements (for example, expanding vapor bubble elements or piezoelectric transducer elements) corresponding to the nozzles and suitable driver and control electronics for controlling the ejection elements. Typically, the one or more arrays of nozzles and the ejection elements along with their associated components are referred to as a print head. It is the activation of the ejection elements that causes drops of ink to be expelled from the nozzles. The ink ejected in this manner forms drops which travel along a flight path until they reach a print medium such as a sheet of paper, an envelope or the like. Once they reach the print medium, the drops dry and collectively form a printed image, such as a Digital Postage Mark (DPM). Typically, the ejection elements are selectively activated (energized) or not activated (not energized) to expel or not expel, respectively, drops of ink as relative movement is provided between the print head and the print medium so that a predetermined or desired print image is achieved.
The postal services of many countries around the world permit and/or require the printing of DPMa that include two dimensional barcodes. DPMs typically include a number of information items in human readable and/or machine readable form, such as, and without limitation, the paid postage amount, the date and time the indicium was generated, the identification number of the postage meter used to generate the indicium, the ascending register value, a postal service symbol, the class of service desired for the mailpiece, the addressee ZIP code and/or address, and the sender's name and/or address. For example, the United States Postal Service has implemented a program known as the Information Based Indicia Program (IBIP) which permits a user to generate a postage indicium for sending a mailpiece (e.g., letter, package, etc.) that includes a human readable portion and a machine readable portion in the form of a two dimensional barcode, such as, without limitation, a Data Matrix symbol.
As is known, a two dimensional barcode, such as a Data Matrix symbol, typically consists of a number of data regions having nominally square modules arranged in an array, wherein each module generally represents one bit of data. For a black on white Data Matrix symbol, for instance, a darkened (i.e., filled) module represents a binary “one” and a light (e.g., empty) module represents a binary “zero.” Each darkened module typically consists of multiple printed pixels. For example, a darkened module may consist of 25 pixels arranged in a 5×5 pixel pattern. In a mailing machine where ink jet printing is used, each drop of ink is a pixel. The data regions in a two dimensional barcode are usually surrounded by a finder pattern which, in turn, is surrounded by a quiet zone border. In addition, multiple data regions may be separated by an alignment pattern.
The two dimensional barcodes employed in many DPMs, such as the Data Matrix symbol in an IBIP indicium, also include encrypted information, such as the postage amount and other postal data relating to the mailpiece and the postage meter that printed the indicium (usually referred to as a digital token or a digital signature), that may be used by the particular postal service in question to authenticate the indicia after the mailpieces have been placed into the mail stream for delivery. However, the improvement of photocopying, printing and scanning equipment over time has made it easier to commit fraud by copying and reusing postal indicia. Thus, there is a need for a system and method for preventing fraudulent duplication and reuse of DPMs that are printed using ink-j et printing technologies.